Recently, increased attention has focused on a new class of peptides, termed atrial natriuretic factor(s), or ANF, which was initially found in atrial tissue extracts. When administered peripherally, potent natriuretic and diuretic effects on the kidney have been produced by this peptide. Histological studies in rat brain have revealed recently that a dense localization of ANF-containing neurons exist in the anteroventral third ventricle, or AV3V area of the brain. Based on these findings, ANF was microinjected into this region of the brain. Blood pressure (BP) and heart rate (HR) responses were monitored to study the physiological significance of the localization of ANF in this region of the brain. The results from this study reveal that pmol quantities of ANF produce substantial increases in both BP and HR. Mean arterial, systolic and pulse pressures as well as HR were significantly elevated by ANF in comparison to the effect produced by a prior injection of saline. Systolic pressure, pulse pressure and HR were found to increase in a dose-dependent manner. The onset of these cardiovascular effects was seen 15-45 min after injection. Peak effects were usually observed approximately 90-120 min after onset, and the duration of these effects was 3-4 h. The results from this study provide evidence for a functional role of ANF in the AV3V area of the brain, and lend support to the idea that ANF may plan an important role in central cardiovascular regulatory mechanisms.